Copolymers, and particularly copolymer and terpolymers rubbers (e.g., ethylene-propylene (EP) rubbers and ethylene/α-olefin/diene rubbers such as ethylene-propylene-diene rubbers (EPDM) rubbers), produced using conventional Ziegler-Natta catalysts based on transition metals may have long chain branching structures. The presence of long-chain branching may lead to improved processability and some improved end-use properties for certain copolymer and terpolymers rubbers such as EP and EPDM rubbers. For instance, long chain branching may result in polymers exhibiting improved melt elasticity, and/or improved shear thinning (indicating polymer that is highly viscous at low shear rates, but less viscous at higher shear rates associated with processing of polymers such as extrusion). However, traditional Ziegler-Natta catalyzed rubbers (e.g., znEPDM) typically have a broader composition distribution (CD), such as a broader inter-chain distribution of ethylene-derived units, which may result in undesirably higher crystallinity. This could impact elasticity properties of rubbers, and/or processability of such rubbers. In addition, Ziegler-Natta processes are frequently more expensive than newer technologies, such as metallocene-based processes.
Metallocene-based copolymers and terpolymers frequently exhibit desirably narrow CD. However, such copolymers and terpolymers typically lack long chain branching, and have narrower molecular weight distribution (MWD), which may adversely affect the performance and processability of metallocene-based copolymer rubbers such as metallocene-based EP rubber (mEP) and metallocene-based EPDM rubber (mEPDM).
Although many metallocene-based copolymers have been reported, such copolymers frequently lack one or more of the desired high molecular weight, large MWD, high CD, and high degree of long chain branching, and/or desired rheological properties frequently associated with long chain branching, particularly in metallocene-based copolymer rubbers such as mEP or mEPDM rubbers.
Along these and similar lines, some relevant publications include those identified in Paragraphs [0005]-[0011] in US Patent Publication No. US 2015/0025209 (incorporated by reference herein); the publications identified in Paragraph [0004] of WIPO Publication No. WO 2015/009832 (incorporated by reference herein); and also the following: US Patent Publication Nos. 2012/0245311, 2014/0051809; U.S. Pat. Nos. 6,506,857, 8,318,998, 8,829,127; and Japan unexamined patent publication Hei 8-239416.
The reported processes and polymers leave much to be desired in terms of the sought-after properties of metallocene copolymers, particularly copolymer rubbers such as mEP and mEPDM. Processes are not known for the production on a commercial scale of metallocene polymer compositions having high Mw, high MWD, and/or desired rheological properties sufficient to compete with more expensive Ziegler-Natta catalyzed polymer compositions. Nor are processes known to produce copolymers such as terpolymers having high Mw, long chain branching, and/or controlled molecular structures incorporating such long-chain branching in a targeted manner, and/or with tuned branch structure and/or composition (e.g., comb-type copolymers with amorphous backbones and semi-crystalline branches, comb-type polymers with semi-crystalline backbones and amorphous branches, copolymers with controlled distribution of diene monomers and/or other monomers, copolymers with controlled branch-length, and the like). Such polymer compositions, for example mEPDM polymer compositions, would be particularly useful for a variety of applications, including traditional EPDM applications in addition to applications such as viscosity index improvers, wire and cable coating, thermoplastic vulcanizate feedstock, tires, and the like.